Lightning strike protection surfacer and method of manufacturing the same

ABSTRACT

A thermoplastic surfacer for providing lightning strike protection to a composite component of an aircraft, methods of manufacturing the surfacer, and methods of applying the surfacer to a composite part. The thermoplastic surfacer includes a broadgood having an amorphous thermoplastic resin, one or more fillers embedded into the broadgood, and a lightning strike protection mesh or foil embedded into the broadgood. When applying the surfacer to a composite part of an aircraft, the method includes draping the surfacer on an at least partially unconsolidated composite part, consolidating the at least partially unconsolidated composite part by heating the part to a temperature at or above a melt temperature of a resins used in the part and in the surfacer, and filling at least one surface defect in the consolidated part using the amorphous thermoplastic polymer resin and milled fibers provided in the thermoplastic surfacer.

BACKGROUND OF THE INVENTION

Composite parts of aircrafts or other vehicles are made from severallayers, or plies, of fibers and resin, which are hardened or cured tomaintain rigidity. These composite parts are relatively lightweight ascompared to traditional metallic parts, while exhibiting similar or evenimproved strength and longevity properties. Thus, many aircraftcomponents such as fuselages, wings, and other parts that traditionallywere made of steel, aluminum, or other metal are now produced ascomposite parts. These composite parts may be formed using athermoplastic polymer, which turns to liquid when heated and turns solidwhen cooled, or else using a thermoset polymer, which is a polymer thatis pliable at room temperatures and thereafter cures when heated toelevated temperatures.

Unlike metal components, however, composite parts are not electricallyconductive, and thus do not inherently provide adequate lighting strikeprotection. When fuselages or wings are made from aluminum, steel, orother metallic substances, the outer surface provides a highlyconductive path such that, if the part is subject to a lightning strikeduring flight, the current passes from the entry point across thesurface to an exit point without structurally damaging the aircraft. Onthe other hand, the materials used to form composite aircraft componentssuch as, for example, carbon or graphite fibers combined with athermoplastic or thermoset resin, are not electrically conductive andthus cannot, on their own, sufficiently pass current across the outerskin of the component.

Composite parts of aircraft in lightning strike zones are thereforeprovided with a lightning strike protection layer, which increases theconductivity of the outer surface of the composite part and enables thecomposite part to sufficiently absorb and pass current from a lightningstrike across the outer surface of the part without structural damage tothe part similar to the more traditional aluminum, steel, or othermetallic components. The lightning strike protection layer may be aconductive metallic mesh or foil that is affixed to the outer surface ofthe composite part. If the part is thereafter subjected to a lightningstrike, the current passes from the entry point to an exit point via theconductive mesh or foil eliminating structural damage to the aircraftpart.

Often, composite parts are created using a thermoset resin, which isrelatively pliable at normal manufacturing temperatures and which curesand hardens when heated to elevated temperatures. For such thermosetparts, adding lightning strike protection may include adding anoutermost layer comprised of a thermoset resin and wire mesh or foil,and then heating the part to cure the thermoset resin thus bonding thewire mesh or foil to the component part and holding the mesh or foil inplace. Because the thermoset resin is pliable at normal manufacturingtemperatures, the lightning strike protection layer can relativelyeasily conform to the outer contour of the wing, fuselage, or otheraircraft part being produced.

Recently, however, there has been a push to produce aircraft componentsfrom thermoplastic polymers because thermoplastic components exhibitcertain advantages over thermoset components. For example, thermoplasticcomponents may be more easily recycled than thermoset components, mayexhibit increased strength as compared to thermoset components, and areless expensive and easier to produce because the parts can be heated andcooled repeatedly and produced rapidly without the need for autoclavesor other expensive equipment.

Thermoplastic component parts have certain drawbacks, however. For one,semi-crystalline thermoplastic composites have a very low surface energyand thus can be difficult to bond with primer or paint. Thus, in orderto achieve sufficient paint adhesion for thermoplastic component parts,the outermost layer must be subjected to slow and expensive surfacetreatment such as plasma or corona etching to achieve a sufficientsurface roughness or surface energy increase for paint adhesion.Similarly, to repair surface defects in thermoplastic parts, additionalsurface treatment (such as etching or similar) is necessary so that thefiller may adequately bond to the defect.

Moreover, the low surface energy of the semi-crystalline thermoplasticparts makes it difficult for the secondary application of lightningstrike protection to a thermoplastic skin in a durable fashion. That is,thermoplastic processing resins that are compatible for simultaneousmelt processing with the composite parts are in the form of a film,which at ordinary manufacturing temperatures are not pliable and thusnot drapable. In this regard, the film must be applied to the compoundcontours of the part being formed (fuselage, wing, etc.) in narrowstrips. When applying a lightning strike protection in the form of ametallic mesh or foil or the like, each strip must form sufficientcontact with the neighboring strip in order to ensure sufficientconductivity across the outer surface of the composite part. Any becausesuch films do not have any tack at normal manufacturing temperatures, itis challenging to keep the narrow strips in place during application andprocessing.

Still more, the high processing (melt) temperature and crystallinecontent of advanced thermoplastic resins results in substantialshrinkage when they cool, especially for a resin rich area. This resultsin substantial residual tensile stress in the resin when processed witha low coefficient of thermal expansion (CTE) carbon fiber laminate thatshrinks very little during cool-down. These stresses can result incracking of the resin, especially when exposed to low temperatures.Furthermore, when complex thermoplastics structures are processed inproduction surface porosity and pitting often occur. Repairing thesedefects can be expensive, especially when they occur in lightning strikeprotected areas.

Thus, although it would be desirable to form certain composite partsfrom thermoplastic polymers, the difficulty in applying a sufficientsurfacer, particularly in lightning strike protected areas, has limitedthe use of thermoplastic component parts in practice. Thus, there existsa need exists for an improved surfacer to be implemented onthermoplastic composite parts.

BRIEF SUMMARY OF THE INVENTION

At a high level, the present invention is directed to an improvedsurfacer to be used with thermoplastic component parts, and methods ofproducing the same. More particularly, embodiments of the invention aredirected to a paintable surfacer for thermoplastic composite laminateswith integral lightning strike protection mesh or foil that has drapeand reinforced surface healing capability, and methods of producing thesame.

For example, some embodiments of the invention are directed to athermoplastic surfacer for providing lightning strike protection to acomposite component of an aircraft. The thermoplastic surfacer includesa broadgood having an amorphous thermoplastic resin, one or more fillersembedded into the broadgood, and a lightning strike protection mesh orfoil embedded into the broadgood.

Other embodiments of the invention are directed to a method ofmanufacturing a thermoplastic surfacer for providing lightning strikeprotection to a composite component of an aircraft. The method includesconveying a matrix resin fleece along one or more conveyor tables, withthe matrix resin fleece including a broadgood having an amorphousthermoplastic resin embedded therein. The method also includes embeddingone or more fillers into the matrix resin fleece and heating the matrixresin fleece until at least a portion of the amorphous thermoplasticresin reaches a melt temperature of the amorphous thermoplastic resin.Finally, the method includes embedding a lightning strike protectionmesh or foil into the matrix resin fleece.

Still other embodiments of the invention are directed to a method ofapplying a thermoplastic surfacer to a composite part of an aircraft.The method includes draping a thermoplastic surfacer on an at leastpartially unconsolidated composite part, such as the thermoplasticsurfacer discussed above or the thermoplastic surfacer produced by themethod discussed above. The method further includes consolidating the atleast partially unconsolidated composite part thereby forming aconsolidated composite part by heating the at least partiallyunconsolidated composite part to a temperature at or above a melttemperature of a resin used in the at least partially unconsolidatedcomposite part and at or above a melt temperature of the amorphousthermoplastic polymer resin of the thermoplastic surfacer. Finally, themethod includes filling at least one surface defect in the consolidatedpart using the amorphous thermoplastic polymer resin and milled fibersprovided in the thermoplastic surfacer.

These and other features will be discussed in more detail below inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to theattached drawing figures, wherein:

FIG. 1 is an elevation view of a first embodiment of tooling used toproduce a thermoplastic surfacer according to aspects of the invention;

FIG. 2 is an elevation view of a second embodiment of tooling used toproduce a thermoplastic surfacer according to aspects of the invention;

FIG. 3 is an elevation view of a third embodiment of tooling used toproduce a thermoplastic surfacer according to aspects of the invention;

FIG. 4 is a plan view of two passes of a thermoplastic surfaceraccording to an aspects of the invention;

FIGS. 5A-5B are elevation views of consolidation tooling including acomposite part having a thermoplastic surfacer according to aspects ofthe invention;

FIG. 6 is a flowchart depicting a method of manufacturing athermoplastic surfacer according to aspects of the invention; and

FIG. 7 is a flowchart depicting a method of applying a thermoplasticsurfacer to a composite part according to aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized,and changes can be made, without departing from the scope of the currentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the current invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment,” “an embodiment,” or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment,” “an embodiment,” or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc., described in one embodimentmay also be included in other embodiments, but is not necessarilyincluded. Thus, the current technology can include a variety ofcombinations and/or integrations of the embodiments described herein.

Generally, aspects of the invention are directed to a thermoplasticsurfacer that overcomes problems associated with using thermoplasticlaminates as primary composite part structures, especially in areaswhere lightning strike protection is required. These and other featureswill be readily understood with reference to the figures.

First, FIG. 1 shows tooling 110 used to manufacture a thermoplasticsurface 132 according to a first embodiment of the invention. Thetooling 110 includes a roll of matrix resin fleece 112 that isultimately injected or impregnated with fillers 118, 120 and lightningstrike protection mesh or foil 128 to form the drapable thermoplasticsurfacer 132.

At a high level, the matrix resin fleece 112 is an amorphous polymerfleece that is similar in terms of drapability and pliability to aconventional blanket or coat-liner type material. More particularly, thematrix resin fleece 112 is an amorphous polymer filament felt made bydistributing and entangling thermoplastic filaments into a widebroadgood—that is, a non-woven fabric made of thermoplastic filaments.Any suitable thermoplastic that exhibits amorphous behavior (as opposedto crystalline or semi-crystalline behavior) can be used as thethermoplastic filaments. These amorphous polymers include, withoutlimitation, acrylonitrile butadiene styrene (ABS), polystyrene (PS),polycarbonate (PC), polysulfone (PSU), polyethersulfone (PES),polyphenylene sulfone (PPSU), and polyetherimide (PEI).

For example, one non-limiting example of a suitable matrix resin fleeceis the backing material used by the Mitsubishi Chemical Corporation isits commercial PEI thermoplastic fleece product marketed under the tradename Kyron®Tex. The Kyron®Tex PEI product generally includes a matrixresin fleece material combined with various reinforcement fibers. Thus,in some embodiments the matrix resin fleece 112 may be the matrix resinfleece portion of the Kyron®Tex PEI product; that is, the matrix resinfleece 112 may be Kyron®Tex PEI without some or all of the reinforcementfibers. In other embodiments the matrix resin fleece 112 may be theKyron®Tex PEI product in its entirety; that is the matrix resin fleece112 could already have glass fibers embedded as is currently availablefrom Mitsubishi.

In some embodiments, the matrix resin fleece 112 will have a melt orhandling temperature similar to the melt or handling temperature of thethermoplastic component part to which the surfacer 132 is ultimately beapplied to assist with adhesion during processing steps such as duringlaminate consolidation, as will be discussed in more detail below inconnection with FIGS. 5A, 5B, and 7. As shown in FIG. 1, the matrixresin fleece 112 may be provided about a roll and thus unrolled alongvarious processing tables 114, 122 during manufacture of thermoplasticsurfacer 132. However, in other embodiments the matrix resin fleece 112may be provided in a different format such as discontinuous, flat sheetsof fleece or otherwise without departing from the scope of theinvention.

The tooling 110 shown in FIG. 1 includes various powder applicators 116and tables 114, 122 used to apply any desired filler 118, 120 to thematrix resin fleece 112. The powder applicators 116 are configured toinfiltrate the matrix resin fleece 112 with the milled fibers 118 and/orthe fillers 120 when the matrix resin fleece 112 is dry and lofty.Namely, the tooling 110 includes an air table 114, a vibration table122, and two powder applicators 116: a milled fiber 118 applicator andother filler 120 applicator. The milled fibers 118 may be any type ofsuitable fiber and in some embodiments may be milled carbon, graphite,and/or glass fibers. The addition of these short or milled fibers 118can provide improved strength properties and can be easily dispersedinto the fleece 112 while it is still lofty. The fillers 120 can providereduced shrinkage, greater wear resistance, UV resistance, impacttoughness, improved strength, higher modulus, improved sand-ability,reduced CTE, increased dielectric strength and other desirableproperties. The fillers 120 can include nanoclay, talc, calciumcarbonate, Kaolin, Wollastonite, mica and many other fillers widely usedwith polymers. In some embodiments the fillers 120 can also includenanotubes, nanonickel strands, and other highly conductive fillers toimprove conductivity of the surfacer 132. These milled fibers 118 and/orother fillers 120 reduce the shrinkage of the surfacer 132 and providegreater resistance to any induced stresses during manufacture and use ofthe surfacer 132. Furthermore, the milled fibers 118 and/or otherfillers 120 can be selected and loaded appropriately to provideelectrical isolation between the lighting strike protection mesh or foil128 and the laminate of the composite part to which the surfacer 132 isapplied, thus enabling the use of aluminum mesh or foil on a carbonlaminate that would otherwise require fiberglass isolation ply in theskin laminate to avoid corrosion caused by the galvanic reaction ofaluminum and carbon.

The matrix resin fleece 112 is guided along the tables 114, 122 andimpregnated with or otherwise combined with the milled fibers 118 and/orother fillers 120. More particularly, in the depicted embodiment themilled fibers 118 and fillers 120 are applied to a top surface of thematrix resin fleece 112 and embedded into the fleece 112 via a vacuumprovided by the air table 114 drawing the fibers 118 and fillers 120into the fleece. As the matrix resin fleece 112 (now impregnated withthe fibers 118 and fillers 120) moves along the tooling 110, a vibrationtable 122 may further embed the fibers 118 and fillers 120 therein byvibrating the impregnated fleece 112, causing the fibers 118 and fillers120 to more compactly settle therein. The tooling may also include abinder spray 124 either at one of the tables 114, 122 or else downstreamthereof, which helps to adhere the fibers 118 and fillers 120 to thefleece 112 and ensures the fibers 118 and/or fillers 120 stay in place.

After the fleece 112 is provided with any milled fibers 118, otherfillers 120, and binder spray 124—referred to herein as the“filler-laden” fleece 112—the filler-laden fleece 112 passes throughheaters 126. The heaters 126 heat at least a portion of the resin in thefiller-laden fleece 112 to a melting or softening point, such that thethermoplastic resin begins to melt and becomes more pliable. In someembodiments only a top surface of the resin (that is, a surface to whicha lightning strike protection mesh or foil 128 is to be applied) in thefiller-laden fleece 112 is heated to the melting point. In otherembodiments, the resin is heated completely through its thickness (thatis, the vertical dimension shown in FIG. 1) to the melting temperature.The heaters 126 also serve to dry or cure the binder spray 124 appliedto the fleece 124.

A lightning strike protection mesh or foil 128 is then applied to anexposed (and melted) upward-facing side of the filler-laden fleece 112.The lightning strike protection mesh or foil 128 can be any metallic,and thus electrically conductive, mesh or foil known in the art. Inembodiments in which the mesh or foil is aluminum and the fibers used inthe laminate of the composite part to which the surfacer 132 is to beapplied are carbon, it may be necessary to electrically isolate the meshor foil 128 from the carbon fibers using the milled fibers 118, theother fillers 120, and/or a veil to reduce corrosion due to the galvanicreaction, which will be discussed in more detail below.

Finally, the filler-laden fleece 112 and lightning strike protectionmesh or foil 128 combination is provided to a pair of calendaring rolls130 which compress the lightning strike protection mesh or foil 128 intothe heated, filler-laden fleece 112 forming the novel thermoplasticsurfacer 132. At this point the matrix resin fleece 112 will bepartially consolidated such that the mesh or foil 128 will be attached,but the resin will not be completely melted so that the right amount ofdrape remains while providing enough support so that the mesh or foil128 is protected from handling damage.

Optionally, once cooled the thermoplastic surfacer 112 can be spooledonto a takeup roll 134 or similar for storage and/or transportation. Insuch embodiments, when ultimately applied to a composite part or thelike, the surfacer 132 is simply spooled off of the takeup roll 134 anddraped onto the composite part.

The thermoplastic surfacer 132 exhibits several advantages as comparedto known surfacers and lightning strike protection processes. Becausethe lightning strike protection mesh or foil 128 is embedded into thematrix resin fleece 112, the mesh or foil 128 is protected duringhandling and when applying to a composite part. Put another way, thecombination of the partially consolidated filled fleece 112 andlightning strike protection mesh or foil 128 (i.e., conductive foil) canprovide drapability and prevents damaging the very fragile foil duringhandling. This prevents damage to the mesh or foil 128 that mayotherwise occur using known manufacturing processes and thus increasesthe integrity of the lightning strike protection features.

Moreover, the thermoplastic surfacer 132 is drapable and thus can morereadily conform to the complex outer contours of the composite part towhich the surfacer 132 is being adjoined. Because known films are notdrapable, they must be applied in strips when accommodating complexcontours with each strip being adjoined to neighboring strips. This mayresult in gaps in the conductive mesh or foil and thus reduced lightningstrike protection performance, defects formed at the intersection ofadjoining strips, and time-consuming and expensive manufacturingprocesses.

Still more, because the resin of the thermoplastic surfacer 132 may havea melt temperature substantially similar to the thermoplastic compositepart to which it is applied, the surfacer 132 may be easily melded withthe composite part during manufacture by simply heating the componentsto the melt range and subsequently cooling. More particularly, themethod of manufacturing the thermoplastic surfacer 132 would begin witha felt or fleece composed of an amorphous resin with a similar processtemperature to that of composite laminate matrix being covered. Ideallythe surfacer and the laminate would have substantial overlap inrecommended process temperatures. For example, the recommended processtemperature for Toray TC 1225 polyaryletherketone (PAEK) carbon prepregis 608 to 720° F. and the Mitsubishi Chemical Kyron®Tex PEI has arecommended process temperature of 680 to 716° F. This overlap ofprocessing temperatures allows the two to melt and diffuse togetherduring laminate consolidation.

Still more, because the thermoplastic surfacer 132 is formed using anamorphous rather than semi-crystalline resin, the outer surface of thethermoplastic surface 132 exhibits increased paint adhesioncharacteristics as compared to the outer surface of thermoplasticcomponent parts made from semi-crystalline resins. Paint, primer, andother substances used to fill surface pitting or defects adheres morereadily to this amorphous resin as compared to semi-crystalline resins.Thus, primer, paint, and other finishing or defect-filling materials canbe easily applied to a composite part outfitted with the thermoplasticsurfacer 132 without necessitating additional processing steps such asetching or the like.

Although FIG. 1 depicts one embodiment of tooling 110 used to create oneembodiment of a thermoplastic surfacer 132 according to aspect of theinvention, other tooling and fillers can be employed resulting inalternative thermoplastic surfacers without departing from the scope ofthe invention. For example, FIG. 2 depicts alternative tooling 210 usedto create a second thermoplastic surfacer 232 according to aspects ofthe invention. The tooling 210 includes a roll of matrix resin fleece212, which is substantially similar to the matrix resin fleece 112discussed in connection with tooling 110 and thus will not be discussedagain in detail. The tooling also includes powder applicators 216including a milled fiber 218 applicator and a filler 220 applicator,which are substantially similar to powder applicators 216 discussed inconnection with tooling 110. Again, the two powder applicators 216 shownin FIG. 2 are for illustrative purposes only and in other embodimentseither of the milled fiber 218 applicator or the filler 220 applicatormay be eliminated from the tooling 220 and/or other powder applicatorsmay be added to the tooling 220 depending on the application withoutdeparting from the scope of the invention. Moreover, although thetooling 220 includes a binder spray 224, which is substantially similarto the binder spray 124, in this embodiment the binder spray 224 isapplied to the matrix resin fleece 112 prior to the milled fibers 218and/or other fillers 220. However, in other embodiments the binder spray224 may be applied to the matrix resin fleece 212 after the powderapplicators 216 without departing from the scope of the invention.

In this embodiment, rather than implementing a vacuum assist table 114to embed the milled fibers 218 and/or other fillers 220 into the matrixresin fleece 212, the tooling 210 uses an electrostatic table 214. Theelectrostatic table 214 includes an electricity source 213 having apositive lead 215 electrically connected to the powder applicators 216in order to make the fillers 218, 220 positively charged and a negativelead 217 attached to a working surface of the table 214 to make thetable 214 negatively charged. In this regard, the positively chargedfillers 218, 220 will be attracted to the negatively charged table 214and become embedded in the matrix resin fleece 212 passing therebetween.The tooling 210 may also include a vibration table 222 in order to morefully embed the fillers 218, 220 into the matrix resin fleece 212, whichis substantially similar to the vibration table 122 discussed inconnection with the tooling 110.

Similar to the filler-laden fleece 112 discussed above, the filler-ladenfleece 212 (i.e., the matrix resin fleece 212 embedded with the milledfibers 218, other fillers 220, and/or binder spray 224) passes throughheaters 226 in order to raise the temperature of the thermoplastic resinto a workability or melting point, and then combined with a lightningstrike protection mesh or foil 228, which is substantially similar tothe lightning strike protection mesh or foil 128 discussed above. Inthis embodiment, however, the lightning strike protection mesh or foil228 is combined with the filler-laden fleece 212 prior to the fleece 212entering the heaters 226. This in turn raises the temperature of boththe fleece 212 and the mesh or foil 128 prior to the components beingpressed together via calendaring rolls 230, which are substantiallysimilar to calendaring rolls 130 discussed above. Heating the mesh orfoil 128 in addition to the filler-laden fleece 212 may reduce stressesand thus defects that may otherwise be caused during cooling of thethermoplastic resin because the heated mesh or foil 228 also cools andthus contracts as the thermoplastic resin cools and contracts. Moreover,the elevated temperature of the mesh or foil 128 may provide for abetter bond between the mesh or foil 128 and the fleece 112 during thecalendaring process. However, in other embodiments the lightning strikeprotection mesh or foil 228 may be applied to the filler-laden fleece212 after the fleece 212 passes through the heaters 226, in a similarmanner as described in connection with tooling 110.

Once the calendaring rolls 230 press the lightning strike protectionmesh or foil 228 into the filler-laden fleece 212 and the thermoplasticresin thereof cools, the thermoplastic surfacer 232 is fully formed.Optionally, the thermoplastic surfacer 232 may thereafter be taken up ona takeup roll 234 or similar for later application to a composite partsuch as a fuselage, wing, or similar component.

FIG. 3 shows tooling 310 used to form yet another embodiment of athermoplastic surfacer 332 according to aspects of the invention. Thetooling 310 generally includes a roll of matrix resin fleece 312, abinder spray 324, a vibration table 322, a lightning strike protectionmesh or foil 328, heaters 326, and calendaring rolls 330, which aresubstantially similar to the matrix resin fleece 112, 212, binder spray124, 224, vibration table 122, 222, lightning strike protection mesh orfoil 128, 228, heaters 126, 226 and calendaring rolls 130, 230,respectively, discussed above and thus will not be discussed in detail.In this embodiment, only one powder applicator 316 is shown—namely, afiller 320 applicator—but in other embodiments additional applicators316 could be utilized without departing from the scope of the inventionincluding a milled fiber applicator (such as the milled fiber 118, 218applicators, discussed above). Moreover, as with tooling 210, in thedepicted embodiment the binder spray 324 is applied to the matrix resinfleece 312 prior to the powder applicators 316 but in other embodimentsthe binder spray 324 could be applied to the fleece 312 after the powderapplicators 316 without departing from the scope of the invention. Stillmore, the tooling 310 implements a roller table 314 followed by thevibration table 322, with the latter most effectively embedding thefillers into the matrix resin fleece 312. However, in other embodimentsadditional tables or processes may be employed to embed any fillers moreeffectively into the matrix resin fleece 312 including vacuum assistedtables such as air table 114 and/or electrostatic table such aselectrostatic table 214.

In this embodiment, the thermoplastic surfacer 332 includes a veil 327between the lightning strike protection mesh or foil 328 andfiller-laden fleece 312. The veil 327 may be a layer of glass or lightfabric or the like used for galvanic isolation when the lightning strikeprotection mesh or foil 328 is comprised of aluminum in order to reduceor eliminate corrosion of the mesh or foil 328 that might otherwiseoccur due to a galvanic reaction between the mesh or foil 328 and thecarbon fibers provided in the thermoplastic composite part to which thethermoplastic surfacer 332 is ultimately applied. In embodiments inwhich the veil 327 is utilized the milled fibers 118, 218 may beeliminated, as shown in FIG. 3, or else the veil 327 may be provided inaddition to the milled fibers 118, 218. In some embodiments the veil 327may be implemented even if the mesh or foil 328 is not aluminum and/orthe fibers of the composite part are not carbon and therefore there isnot a concern of a galvanic reaction, but the veil 327 is nonethelessused in place of the milled fibers 118, 218 or the like for rigidity orother purposes.

The veil 327 is spooled onto the matrix resin fleece 312 prior to thelightning strike protection mesh or foil 328 in order to provide anultimate electric barrier between the mesh or foil 328 and the carbonfibers. Although in the depicted embodiment the veil 327 and the mesh orfoil 328 are spooled onto the filler-laden fleece 312 prior to theheaters 326, in other embodiments one or both of the veil 327 and thelightning strike protection mesh or foil 328 may be spooled onto thefiller-laden fleece 312 after the fleece 312 has passed through theheaters 326. Finally, the veil 327 and mesh or foil 328 are thereaftercompressed into the heated fleece 312 via the calendaring rolls 330forming the thermoplastic surfacer 332, and optionally spooled onto atakeup roll 334 for later use, as discussed.

In some embodiments, the width of the lightning strike protection meshor foil 128, 228, 328 being applied to the filler-laden fleece 112, 212,312 may be smaller than or equal to the width of the filler-laden fleece112, 212, 312. As used herein, “length” refers to the substantiallycontinuous dimension of the fleece 112, 212, 312 as is comes off theroll (corresponding to the horizontal direction as viewed in FIGS. 1-4),while “width” refers to the greater of the two dimensions of the fleece112, 212, 312 perpendicular to the length (corresponding to the verticaldirection as viewed in FIG. 4 and a direction perpendicular to thehorizontal direction and vertical direction in FIGS. 1-3). However, inother embodiments the width of the lightning strike protection mesh orfoil 128, 228, 328 may be greater than the width of the filer-ladenfleece 112, 212, 312 in order to increase electrical continuity betweenneighboring lengths of surfacer 132, 232 when applied to a compositepart in an lightning strike zone.

This may be more readily understood with reference to FIG. 4, which is aplan view of two lengths of the thermoplastic surfacer 132 a, 132 bdiscussed in connection with FIG. 1. Although for simplicity thefollowing discussion is made in view of surfacer 132, the otherembodiments of the thermoplastic surfacer discussed herein including thesurfacers 232, 332 could similarly include lightning strike protectionmesh or foil 228, 328 having a width greater than the fleece 212, 312 towhich the mesh or foil 228, 328 is being applied in order to achievesimilar conductivity benefits.

The thermoplastic surfacers 132 a, 132 b each include a filler-ladenfleece 112 a, 112 b having a first width, w₁, and a lightning strikeprotection mesh or foil 128 a, 128 b having a second width, w₂, which isgreater than w₁. Because w₂ is greater than w₁, the mesh or foil 128overhangs the fleece 112 forming a mesh or foil overhang 410 a, 410 b.When the thermoplastic surfacers 132 a, 132 b are applied to a compositepart or the like such that the adjacent passes of the fleece 112 a, 112b abut each other, the mesh or foil overhang 410 a of the first surfacer132 a overlaps the second surfacer 132 b forming an overlapping region412. Put another way, the protruding mesh or foil 128 a on one edge ofthe first surfacer 132 a can be covered by the next pass of the secondsurfacer 132 b, creating direct electrical contact between the rows ofthe thermoplastic surfacer 132 a, 132 b. In this regard, there is nothreat of a residual gap being formed in the mesh or foil 128 when thesurfacer 132 is applied to a composite part in strips. Moreparticularly, the lightning strike protection mesh or foil 128 a of thefirst surfacer 132 a forms a electric bond with the lightning strikeprotection mesh or foil 128 b of the second surfacer 132 b due to theoverlap 412, ensuring electrical continuity between the surfacers 132 a,132 b. Thus, when present in a potential lightning strike zone on anaircraft of the like, the overlapping mesh or foils 128 a, 128 b ensurethat any lightning strike is effectively routed across the surface ofthe aircraft from an entry point to an exit point without damaging thecomposite skin of the aircraft that may otherwise occur if there is abreak between successive mesh or foils.

Applying a thermoplastic surfacer made in accordance with aspects of theinvention such as the surfacers 132, 232, or 332 or similar maybeneficially provide automatic defect filling during consolidation of alightning strike protected part. This may be more readily understoodwith reference to FIGS. 5A and 5B. These figures generally showconsolidation tooling 510 using to consolidate a composite part 511 madefrom multiple plies of thermoplastic resin and fiber fillers. Prior toconsolidation, which is depicted in FIG. 5A, the composite part 511generally includes a pre-consolidated stiffener 512 and unconsolidatedlaminate 514, which includes multiple plies of fiber and thermoplasticresin. The composite part 511 also includes a thermoplastic surfacer 522(which may be the thermoplastic surfacer 132, 232, or 332 or similar)applied to an outer-facing surface of the unconsolidated laminate 514;that is, a surface of the composite part 511 that will ultimately faceoutwardly and thus be painted, be vulnerable to lightning strikes, etc.The surfacer 522 in laid upon a consolidation tool 520 such as a tableor the like, and the entire part is covered with a vacuum bag 517. Thevacuum bag 517 is generally a plastic sheet or the like and isconfigured to cover the composite part 511 during consolidation in anairtight manner. In this regard, a sealant tape 518 or similar may beprovided around the open edges of the vacuum bag 517 forming an airtightseal.

During consolidation, the composite part 511 is heated while a negativepressure (i.e., vacuum) is applied to the vacuum bag 517 via a vacuum516. As the air is removed from the vacuum bag 517, the vacuum bag 517exerts pressure on the unconsolidated laminate 514 forcing it tocompress, or consolidate, after which the composite part 511 is readyfor painting and/or assembly into the aircraft. Because the stiffener512 is preconsolidated, however, it does not further compress during theconsolidation process. And because the laminate portion 514, 515 thusshrinks during consolidation while the stiffener does not, sometimesdefects can form in the composite part 511 during the consolidationprocess, such as a vacuum bag induced defect 524 shown in FIG. 5B, orother defects such as surface pits or grooves.

Traditionally, these defects must be filled or otherwise repairedfollowing the consolidation process, which can be time-consuming.However, the surfacer 522 made according to aspects of the invention mayserve to self-fill these defects, resulting in a smooth outer surface ofthe composite part 511 without further finishing and defect repair. Moreparticularly, during the consolidation process resin from the surfacer522 flows from an area of high pressure to any areas of low pressure andthus into any defects such as the vacuum bag induced defect 524, forminga resin pocket 526 that fills the void and otherwise prevents anoticeable defect on the outer surface of the consolidated laminate 515.Moreover, the resin pocket 526 will include fillers and fibers 528 (suchas, e.g., the milled fibers 118, 218 or other fillers 120, 220, 320)thereby reducing shrinkage of the resin pocket 526, reducing residualtensile stresses in the resin pocket 526, and otherwise providingincreased tensile strength and crack resistance to the resin pocket 526.Still more, because the resin and any fillers and fibers 528 includedtherein fills the defect 524, the lightning strike protection mesh orfoil 530 of the surfacer 522 does not get pulled into the defect. Thiseliminates possible damage to the mesh or foil 530 that may otherwiseoccur if the resin did not fill the defect 524.

FIG. 6 is a flowchart of an exemplary method 600 of manufacturing athermoplastic surfacer such as surfacers 132, 232, or 332 according toaspects of the invention. First at step 610 a matrix resin fleece isprovided. As should be appreciated from the above discussion, the matrixresin fleece is a wide broadgood or felt including a suitable amorphousthermoplastic resin including, without limitation, ABS, PS, PC, PSU,PES, PPSU, and PEI.

At step 620 the matrix resin fleece is embedded with any desired fillerssuch as milled fibers or the like via one more powder applicators suchas applicators 116, 216, 316. These fillers can include, but are notlimited to, nano clay, talc, calcium carbonate, Kaolin, Wollastonite,mica, other fillers widely used with polymers, nanotubes, nanonickelstrands, highly conductive fillers, and milled fibers such as glass,carbon, or other suitable fibers. Moreover, optionally a vacuum assisttable, electrostatic table, vibration table, and/or other electronicallyor mechanically controlled tooling can be used at step 620 to assistembedding the fibers into the matrix resin fleece.

At step 630 a binder spray is applied to the matrix resin fleece. Asshould be appreciated from the above discussion in connection with FIGS.1-3, in some embodiments the binder spray is applied to the matrix resinfleece after the addition of any desired fillers or milled fibers, whilein other embodiments the binder spray may be applied prior to theaddition of any desired fillers or milled fibers.

At step 640 a lightning strike protection mesh or foil is applied to thefiller-laden matrix resin fleece. This may be any lightning strikeprotection mesh or foil typically used in lightning strike zones on anaircraft fuselage or wings or the like. In embodiment in which carbonfibers are used in the composite part to which the surfacer is to beapplied, a veil may also be applied at step 640. In such embodiments theveil is placed between the lightning strike protection mesh or foil andthe filler-laden fleece in order to mitigate corrosion due to thegalvanic reaction between the metallic mesh or foil and the carbonfibers. Moreover, and as discussed in connection with FIG. 4, the meshor foil and optional veil may be wider than the matrix resin fleece towhich the mesh or foil is being applied so that the mesh or foiloverhangs the fleece and overlaps the mesh or foil of neighboringsurfacer components when ultimately applied to a composite part or thelike ensuring conductivity between the multiple lengths of surfacers.

At step 650 the filler-laden mesh or foil is heated so that at least thesurface of fleece reaches the melt temperature. Optionally, the matrixresin fleece can be heated throughout such that all of the thermoplasticresin reaches the melt temperature. Moreover, in some embodiments thefiller-laden fleece is heated prior to the addition of the lightningstrike protection mesh or foil and optional veil (that is, in someembodiments step 650 is performed prior to step 640), while in otherembodiments the lightning strike protection mesh or foil and optionalveil are applied to the filler-laden mesh or foil and optional mesh orfoil prior to the heating step such that the mesh or foil, optionalveil, and filler-laden fleece are all heated at step 650.

At step 660 the lightning strike protection mesh or foil and optionalveil are compressed into the filler-laden fleece such as by, withoutlimitation, calendaring the lightning strike protection mesh or foil andoptional veil into the filler-laden fleece as discussed above. Oncefully cooled, the surfacer is complete and ready for applying to acomposite thermoplastic part. Optionally, the completed thermoplasticsurfacer can be spooled onto a takeup spool such as spool 134, 234, 334for storage or transportation.

FIG. 7 is a flowchart of an exemplary method 700 of applying athermoplastic surfacer such as surfacers 132, 232, or 332 to a compositepart such as composite part 511 according to aspects of the invention.At step 710 a composite part with at least one unconsolidated componentis provided. The composite part include multiple layers, or plies, of afiber encased in a thermoplastic resin.

At step 720 a thermoplastic surfacer such as the thermoplastic surfacer132, 232, 332 discussed above is applied to an outer-facing surface ofthe composite part. Again, the thermoplastic surfacer is drapable andthus can seamlessly be applied to the thermoplastic composite partnotwithstanding any complex contours of the part. In some embodimentsthe thermoplastic surfacer is applied piecewise to a large compositepart, with each length of surfacer abutting a neighboring surfacer. Inembodiments in which the lightning strike protection mesh or foiloverhangs the edge of the matrix resin fleece such as the embodimentsshown in FIG. 4 above, at step 720 the overhanging mesh or foil isoverlaid on a neighboring length of surfacer forming an overlap oflightning strike protection mesh or foil such as the overhang 412.

At step 730 the composite part with surfacer applied thereto is placedin a consolidation tool. In some embodiments, this may include placingthe outward-facing surface of the part (that is, the surface of the partcontaining the surfacer) against a similarly contoured consolidationtool and placing a vacuum bag around the part. In some embodiments, openedges of the vacuum bag may be sealed to the consolidation tool using asealant tape or the like forming an airtight seal.

At step 740 the unconsolidated portion of the composite part isconsolidated by applying heat and/or a negative pressure to thecomposite part. For example, a vacuum may be used to remove the air fromthe inside of the bag and thus apply a pressure to the unconsolidatedpart while the part is heated to a melting temperature of thethermoplastic resin used in the composite part and/or the surfacer. Asdiscussed in connection with FIGS. 5A and 5B, in some instances theconsolidation process may form a defect on the outer surface of thecomposite part such as, by way of example, the vacuum bag induced defect524 shown in FIG. 5.

At step 750, any defects that are formed in the outer-facing surface ofthe composite part can be self-filled during the consolidation processby the thermoplastic surfacer. More particularly, resin from thesurfacer flows into the defect forming a resin pocket such as surfacerresin pocket 526 discussed above, thereby filling and repairing thedefect. Moreover, in embodiments in which the surfacer includes milledfibers or other fillers, the milled fibers and/or fillers flow into theresin pocket with the thermoplastic resin thus providing increasedstrength to the otherwise resin-rich area.

Finally, at step 760 the composite part is cooled and is then ready forassembly onto an aircraft of the like. Optionally, the composite partwith the surfacer thereon is painted at step 760. As discussed, becausethe surfacers created according to aspects of the invention includeincreased paint adhesion properties as compared to known thermoplasticcomponent parts due to the use of an amorphous thermoplastic resin, thefinished composite part can be primed and painted at step 760 withoutrequiring the slow and expensive surface treatment processed such asplasma or corona etching to achieve a sufficient surface roughness forpaint adhesion.

Although the invention has been described with reference to theembodiments illustrated in the attached drawings, it is noted thatequivalents may be employed without departing from the scope of theinvention as recited in the claims.

What is claimed is:
 1. A thermoplastic surfacer for providing lightningstrike protection to a composite component of an aircraft, thethermoplastic surfacer comprising: a broadgood including an amorphousthermoplastic resin; one or more fillers embedded into the broadgood;and a lightning strike protection mesh or foil embedded into thebroadgood.
 2. The thermoplastic surfacer of claim 1, wherein thebroadgood is composed of thermoplastic fibers in the form of a drapablenonwoven fleece or felt.
 3. The thermoplastic surfacer of claim 1,wherein the one or more fillers include at least one of milled glassfibers, milled graphite fibers, milled carbon fibers, nanoclay, talc,calcium carbonate, Kaolin, Wollastonite, mica, nanotubes, or nanonickelstrands.
 4. The thermoplastic surfacer of claim 1, wherein the amorphousthermoplastic resin is one of acrylonitrile butadiene styrene (ABS),polystyrene (PS), polycarbonate (PC), polysulfone (PSU),polyethersulfone (PES), polyphenylene sulfone (PPSU), and polyetherimide(PEI).
 5. The thermoplastic surfacer of claim 1 further comprising abinder spray configured to bind the one or more fillers to thebroadgood.
 6. The thermoplastic surfacer of claim 1 further comprising aveil abutting the lightning strike protection mesh or foil.
 7. A methodof manufacturing a thermoplastic surfacer for providing lightning strikeprotection to a composite component of an aircraft, the methodcomprising: conveying a matrix resin fleece along one or more conveyortables, the matrix resin fleece comprising a broadgood having anamorphous thermoplastic resin embedded therein; embedding one or morefillers into the matrix resin fleece; heating the matrix resin fleeceuntil at least a portion of the amorphous thermoplastic resin reaches amelt temperature of the amorphous thermoplastic resin; and embedding alightning strike protection mesh or foil into the matrix resin fleece.8. The method of claim 7 further comprising applying a binder spray tothe matrix resin fleece, the binder spray configured to adhere the oneor more fillers to the matrix resin fleece.
 10. The method of claim 8,wherein the binder spray is applied to the matrix resin fleece prior tothe step of embedding the one or more fillers into the matrix resinfleece.
 11. The method of claim 8, wherein the binder spray is appliedto the matrix resin fleece after the step of embedding the one or morefillers into the matrix resin fleece.
 12. The method of claim 7, whereinthe broadgood is composed of thermoplastic fibers in the form of adrapable nonwoven fleece or felt.
 13. The method of claim 7, wherein thestep of embedding the one or more fillers into the matrix resin fleeceincludes embedding at least one of milled carbon fibers, milled graphitefibers, milled glass fibers, nanoclay, talc, calcium carbonate, Kaolin,Wollastonite, mica, nanotubes, or nanonickel strands into the matrixresin fleece.
 14. The method of claim 7, wherein the step of embeddingthe one or more fillers into the matrix resin fleece includes using atleast one of a vacuum assisted table, an electrostatic table, or avibration table to embed the one or more fillers into the matrix resinfleece.
 15. The method of claim 7, wherein the step of embedding thelightning strike protection mesh or foil into the matrix resin fleeceincludes calendaring the lightning strike protection mesh or foil intothe matrix resin fleece.
 16. The method of claim 7 further comprisingembedding a veil into the matrix resin fleece.
 17. The method of claim 7further comprising heating the lightning strike protection mesh or foilprior to the step of embedding the lightning strike protection mesh orfoil into the matrix resin fleece.
 18. The method of claim 7 furthercomprising cooling the matrix resin fleece with the lightning strikeprotection mesh embedded therein and spooling the thermoplastic surfaceronto a takeup roll.
 19. A method of applying a thermoplastic surfacer toa composite part of an aircraft, the method comprising: draping athermoplastic surfacer on an at least partially unconsolidated compositepart, the thermoplastic surfacer including a broadgood including anamorphous thermoplastic resin, milled fibers embedded into thebroadgood, and a lightning strike protection mesh or foil embedded intothe broadgood; consolidating the at least partially unconsolidatedcomposite part thereby forming a consolidated composite part by heatingthe at least partially unconsolidated composite part to a temperature ator above a melt temperature of a resin used in the at least partiallyunconsolidated composite part and at or above a melt temperature of theamorphous thermoplastic polymer resin of the thermoplastic surfacer; andfilling at least one surface defect in the consolidated part using theamorphous thermoplastic polymer resin and milled fibers provided in thethermoplastic surfacer.
 20. The method of claim 19 further comprisingsurrounding the at least partially unconsolidated composite part and thethermoplastic surfacer with a vacuum bag and applying a vacuum pressureto the at least partially unconsolidated composite part and thethermoplastic surfacer.